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Molecular phylogenetics of the Diprotodontia (kangaroos, wombats, koala, possums, and allies)

Osborne, MJ, Christidis, L & Norman, JA 2002, Molecular Phylogenetics and Evolution, vol. 25, pp. 219-228.

The evolutionary relationships of diprotodontid order marsupials (kangaroos, wombats, koala, possums and others) were analysed using ND2 mitochondrial sequences. The findings were also compared with 12S ribosomal DNA (rDNA) sequences. Groupings of organisms descending from a common ancestor, or monophyly, were found for Burramyoidea, Phalangeroidea, Petauroidea, Tarsipedoidea, Macropodoidea and the Vombatiformes (wombats and koala) sub-orders and super-families. Discrepancies between genetic findings and current taxonomic ranks were found.

  ND2 is a mitochondrial gene for nicotinamide dehydrogenase sub-unit two that is 1040 base pairs long. Sequences of 22 diprotodontid order species had variability at 556 nucleotides of ND2 gene, which were used as the basis of further phylogenetic grouping. Sequence variation from 23% to 37.83% was found in the super-families Burramyoidea, Petauroidea, Phalangeroidea, Tarsipedoidea, Macropodoidea, Vombatoidea and Phascolarctoidea (koala). The koala (Phascolarctos) and wombat (Vombatus) super-families had 23.38% variance in the ND2 sequence. Phylogenetic analyses of ND2 and 12S rDNA genes revealed Vombatiformes as a separate group with a common ancestor. Additional analyses showed a close relationship between Macropodoidea (kangaroos), Phalangeroidea (possums), and Vombatiformes, while others showed Vombatiformes as being at the base of the evolutionary tree of the Diprotodontia order.

  Although ND2 sequences had many variations, analysis was still possible deeming ND2 a suitable gene for phylogenetic evaluation. Studies utilising morphology, serology and DNA hybridisation confirm the Vombatiformes suborder as monophyletic, and potentially not requiring further splitting into Vombatus and Phascolarctos. Morphological and DNA hybridisation evidence also supports Vombatiformes’ position at the base of Diprotodontia’s phylogenetic tree. Vombatiformes have a relatively low genetic divergence of 23%, which it is not consistent with current taxonomic divisions that tends to over-split Vombatus and Phascolarctos.

  The findings of this study contribute to our understandings of the evolution of the koala and related marsupials. This new information is useful for the revision of taxonomic ranks and evaluations of genetic distance among the diprotodontids.


Summarised by Alexandra Selivanova


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